Christine Marie Blaumueller

Intracellular Cleavage of Notch Leads to a Heterodimeric Receptor on the Plasma Membrane

Previous models for signal transduction via the Notch pathway have depicted the full-length Notch receptor expressed at the cell surface. We present evidence demonstrating that the Notch receptor on the plasma membrane is cleaved. This cleavage is an evolutionarily conserved, general property of Notch and occurs in the trans-Golgi network as the receptor traffics toward the plasma membrane. Although full-length Notch is detectable in the cell, it does not reach the surface. Cleavage results in a C-terminal fragment, N(TM), that appears to be cleaved N-terminal to the transmembrane domain, and an N-terminal fragment, N(EC), that contains most of the extracellular region. We provide evidence that these fragments are tethered together on the plasma membrane by a link that is sensitive to reducing conditions, forming a heterodimeric receptor.

Human homologs of a Drosophila Enhancer of Split gene product define a novel family of nuclear proteins

Notch and the m9/10 gene (groucho) of the Enhancer of split (E(spl)) complex are members of the “Notch group” of genes, which is required for a variety of cell fate choices in Drosophila. We have characterized human cDNA clones encoding a family of proteins, designated TLE, that are homologous to the E(spl) m9/10 gene product, as well as a novel Notch–related protein. The TLE genes are differentially expressed and encode nuclear proteins, consistent with the presence of sequence motifs associated with nuclear functions. The structural redundancy implied by the existence of more than one TLE and Notch–homologous gene may be a feature of the human counterparts of the developmentally important Drosophila Notch group genes.